1. Field of the Invention
This invention is related to light emitting diode (LED) light extraction for optoelectronic applications.
2. Description of the Related Art
Wafer bonding technology using different combinations of materials, such as InP/GaAs, AlGaInP/GaP, GaAs/GaN, ZnSSe/GaN, has been studied for applications of optoelectronic integration, light emitting diodes (LEDs), vertical cavity surface emitting lasers (VCSELs), and electronic devices (Appl. Phys. Lett. 56, 737-39 (1990); Appl. Phys. Lett. 64, 2839-41 (1994); Appl. Phys. Lett. 81, 3152-54 (2002); and J. J. Appl. Phys. 43, L1275-77 (2004)).
In a nitride LED system, there are several reports of fabricating transparent electrodes on a p-type GaN layer. The general method is to use thin metals of Ni and Au (J. J. Appl. Phys. 34, L797-99 (1995)). Because of the light absorption in the metal, transmittance is only around 60%. Also, surface feature shaping for improving light extraction efficiency is difficult because of the hardness of GaN material and the instability of p-type GaN conductivity.
Another approach is to use ZnO layer growth on p-type GaN (J. J. Appl. Phys. 43, L180-82 (2004)). However, this method requires ZnO crystal growth equipment, which uses ultra-high vacuum conditions. Moreover, it is difficult to grow thick layers, e.g., 500 μm thick layers, that are suitable for feature shaping for the purpose of light extraction.